1. Field of the Invention
The present invention relates to a method for measuring the chromaticity values in a colorimeter and, more particularly, to a measuring method that can get the accuracy level of the measured chromaticity values up to the spectrum mode colorimeter but does not need to use the filters with color-matching functions that are difficult to be deposited and manufactured and is cheaper than the spectrum mode colorimeter.
2. Description of Related Art
A colorimeter is used to measure the data of color performance of an object in different appropriate standard lighting environments. The colorimeter can objectively measure the color of different objects, for example, the reflective surface of plastics, paint, coating, printing, etc., for achieving the control, duplication and delivery of colors effectively. Therefore, the colorimeter is one of the important instruments regardless of the industrial application or the academic research.
In order to quantify and define color by a scientific way, Commission International del'Eclairage (CIE) established a color-matching function x(λ), y(λ) and z(λ) under an equal energy condition in 1931. The appeared color of any illuminated object, such as the spectral intensity of an illuminant S(λ) and the reflectance of the object R(λ), can be calculated by the color-matching function based on XYZ color basis. The XYZ color space is named the CIE 1931 color space system. It is inconvenient in analysis and in applications to depict color coordinates on three-dimensional coordinates as getting a group of XYZ color coordinate data and considering the position in the coordinate space. Based on the concept of the luminance normalization, the equation of an xy color coordinate is first defined as x+y+z=1 while dealing with XYZ color coordinate. The color space defined by x and y is named CIE xy chromaticity diagram.
Nowadays, the measurement of the chromaticity values by a reflection mode colorimeter is according to the standard CIE method to compute the total energy by the reflective light of the object, the CIE color-matching function and a weighting consideration on different wavelengths. The individual chromaticity values depend on the computed total energy and the different color-matching function is obtained.
The foregoing procedure, such as the weighting of color-matching function and the summation of the stimulus energy, can be generalized and divided into two classifications at the design principle.
A. Filter Mode Colorimeter:
Referring to FIG. 7, the filter mode colorimeter cooperates with a specific standard illuminant 20, such as CIE standard illuminant A, CIE standard illuminant C, CIE standard illuminant D, etc., and the specific standard illuminant 20 illuminates on the surface of an object 21. A reflective light 22 that reflects from the surface of the object 21 passes through filters 23 of the color-match functions and is received separately by a multi-band power meter 24. The chromaticity values of the object 21 are obtained afterwards.
However, the marketed standard illuminant D is not accurate enough, and the filters 23 of the color-matching functions are difficult to be deposited and manufactured. The measured chromaticity values are not easy to measure at an accurate level.
B. Spectrum Mode Colorimeter:
Referring to FIG. 8, an object 31 is illuminated by a known white light illuminant 30, and a reflective light 32 that reflects from the surface of the object 31 is received. The reflection index of the object 31 is computed by a spectrometer 33 in a colorimeter. The chromaticity values of the object 31 illuminated on the different standard illuminants will be figured out through the calculation of the colorimeter.
However, the spectrum mode colorimeter is more expensive even though a more accurate chromaticity values of the object can be computed by the spectrum mode colorimeter.
There are some drawbacks in the conventional technologies. For example, the measured chromaticity values by the filter mode colorimeter that is equipped with the marketed standard illuminant D is not accurate enough. Besides, the filter of the color-matching function used to receive the reflective light is difficult to be deposited and manufactured and is inconvenient for mass production.
In addition, the more accurate chromaticity values are obtained through the reflective light received by the spectrometer in the spectrum mode colorimeter. However, the spectrometer is more expensive and is not agreeable to the consideration of the economic benefits.
Due to the drawbacks of the conventional colorimeters, the investigation and research was taken for solving the problems of the colorimeter based on the experiences of research and manufacture in the industrial field. Finally, a method measures the chromaticity values by a colorimeter and exactly improves the above-mentioned drawbacks.